The present invention relates generally to serial interconnect and shared bus methods and systems and, more particularly, to a dynamic perimeter circular bus method and system.
Serial interconnect has become the industry standard for systems having large bandwidth requirements. Serial interconnect has been chosen over shared bus architectures in many cases because of the scalability, physical reach, pin efficiency, and flexibility associated with it. Unfortunately, some of the desirable characteristics of a shared bus, such as low latency, are lost when using serial interconnect in place of shared bus.
There are many situations where the low latency advantages of a shared bus and the reconfiguration and scaling advantages of serial interconnect are needed. An arbitration function in a system is an example of a function that benefits from the low latency characteristics of a shared bus. The speed at which arbitration is performed often defines system performance. In many cases the arbitration algorithm is simple and a large portion of the time spent doing arbitration is associated with communicating with the entities requiring the system resources. The latency of each communication becomes a very significant factor in arbitration speed and consequently system performance. A shared bus is a good candidate to provide the low latency characteristics that are desired for arbitration. Not only are the latency characteristics of the shared bus attractive for arbitration, but the shared media aspect of the bus forces the sequential servicing of requests keeping arbitration orderly and efficient. Unfortunately, shared bus systems are fixed in both physical topology and bandwidth. These two limiting aspects are overcome with the use of serial interconnect.
Arbitration is just an example of control functions that require low latency but are constrained in performance and reach by a shared bus implementation.
There is a strong desire to use a platform for a variety of applications thus implying widely varying system performance requirements. Serial interconnect affords systems the ability to scale in data bandwidth and topology. The beneficial characteristics of a shared bus are not provided by serial interconnect to date. Thus, there exists a need for an interconnect technology that would give a system the ability to scale in data bandwidth as well as the control functionality.
Accordingly, it is an object of the present invention to provide a dynamic perimeter circular bus method and system for transferring loop words between elements connected in a serial loop topology.
It is another object of the present invention to provide a dynamic perimeter circular bus method and system for transferring control loop words between elements connected by a serial control loop running through a serial interconnect.
It is a further object of the present invention to provide a dynamic perimeter circular bus method and system for transferring control and data signals between elements connected by respective serial control and data loops running through a serial interconnect.
In carrying out the above objects and other objects, the present invention provides a method for transferring a loop word between a plurality of elements interposed within a serial loop. The method includes transferring a sync character of the loop word from element to element along the serial loop. The sync character is indicative of the beginning of the loop word. At least one present character of the loop word after the sync character is then transferred from element to element along the serial loop. A present character is then asserted at an element to indicate that a data word follows the asserted present character in the loop word. The data word from the element is then put on to the loop word after the asserted present character. The data word of the loop word is then transferred from element to element along the serial loop.
Preferably, the method includes de-asserting a present character of the loop word at an element to indicate lack of a data word following the de-asserted present character in the loop word. The method further includes removing the data word from the loop word at the element after the data word has been transferred along the serial loop to the element.
Preferably, each element is provided with a shift register. Putting a data word onto the serial loop from an element includes putting the data word into the shift register of the element, switching the shift register into the loop, and then shifting the data word from the shift register of the element onto the serial loop.
In carrying out the above objects and other objects, the present invention further provides a system having a serial interconnect and a plurality of elements for carrying out the method of the present invention.